Resonance suppressing method and apparatus

ABSTRACT

Resonance effects otherwise possibly occuring upon a change in energization of an unloaded power transformer having leads connected in a main alternating current electrical circuit are suppressed through the temporary connection of a resonance suppressing impedance between a lead of the transformer and an electrical ground, with such electrical connection being maintained only through a change in the state of energization of the unloaded transformer.

United States Patent Wolf [451 May 30, 1972 [54] RESONANCE SUPPRESSINGMETHOD AND APPARATUS [72] Inventor: Herman B. Wolf, Charlotte, NC.

[73] Assignee: R. H. Bouligny, Inc., Charlotte, NC.

[22] Filed: Nov. 23, 1970 [21] App]. No.: 91,939

521 u.s.c1 ..317/14,33s/s7,33s/324, 317/16 51 1m.c1. ..11o2117/o4 5sFieldofSearch ..338/57,58,324;317/14, 15, 317/16 [56] References CitedUNITED STATES PATENTS 2,081,894 5/1937 Meyer ..33s/324x 2,087,340 7/1937Davis ..3 1 7/14 B Primary Examiner-D. X. Sliney Attorney-Parrott, Bell,Seltzer, Park 8:. Gibson [57] ABSTRACT Resonance efiects otherwisepossibly occuring upon a change in energization of an unloaded powertransformer having leads connected in a main alternating currentelectrical circuit are suppressed through the temporary connection of aresonance suppressing impedance between a lead of the transformer and anelectrical ground, with such electrical connection being maintained onlythrough a change in the state of energization of the unloadedtransformer.

5 Claims, 3 Drawing Figures TRANSFORMER,

Patented May 30, 1972 3,666,991

TQANSFORMER,

HEQMAN 3. WOLF ATTORNEYS INVENTOR.

, through transformer banks which reduce a relatively highertransmission voltage to a relatively lower voltage appropriate for thecustomers power needs. Particularly in connection with residential powersupply systems, such transformer banks are now commonly connected withunderground cable. Such use of underground'cable has particularlyemphasized and pointed out a difficulty which arises due to the normalcapacitance present between a power conducting cable and electricalground. In particular, it is usually desirable to energize a transformerbefore a secondary load is applied thereto. Where the energization of atransformer is changed by closing and opening single phase cutouts ordisconnects at the source end of connecting cables, the transformerwinding inductance and cable to ground capacitance may lead tooccurrence of ferroresonance efiects. Such resonance effects may resultin damage to protective equipment, damage to the transformer, or damageto the cable. Further, such resonance effects involve variances fromnormal operating frequencies which may produce sounds and other sensedeffects which are disconcerting to operating personnel.

Heretofore, such ferroresonance effects have been minimized or avoidedby the purchase of special transformers or by the temporary connectionof an artificial load to the secondary side of a transformer prior to achange in the energization thereof. Such approaches have suffered fromdeficiencies and difficulties, in that the equipment required isrelatively more expensive than conventional power equipment and theartificial loads imposed require handling of a relatively largeresistance installation in order to be effective for suppressingferroresonance through loading of the transformer.

ln view of the above, it is an object of the present invention tosuppress ferroresonance effects of the type described while facilitatingthe adoption and use of the present invention. This object is realizedthrough a method which is readily practiced by linemen and other fieldpersonnel, so as to thereby be readily incorporated into standardoperating procedures for energizing or de-energizing power transformers.Further, the present invention particularly contemplates use of readilyportable means which may easily be carried in an equipment truck forusage as maybe required. I

A further object of the present invention is the provision of a portableresonance suppressing apparatus which may readily and quickly be appliedbya lineman or other field personnel to suppress resonance effects ofthe type described above, thereby reducing the capital investmentrequired to avoid the deleterious effects of occurrence of suchferroresonance. In accomplishing .this object of the present invention,a resonance suppressing impedance means is arranged for ready temporaryelectrical connection with elements of a main alternating currentelectrical circuit, in parallel with the capacitance of a transformerlead to ground. By such connection of the impedance means, any resonanceeffect appearing on the lead upon a change in energization thereof isdamped while the size and cost of the apparatus which thereby controlsresonance effects are-kept within bounds.

Some of the objects and advantages of the invention having been stated,others will appear as the description proceeds, when taken in connectionwith the accompanying drawings, in which FIG. 1 is a perspective view,partially schematic, of a portion of a power supply system illustratingused the present invention;

FIG. 2 is an enlarged elevation view, in section, of the resonancesuppressing apparatus of the present invention; and

FIG. 3 is a schematic diagram of a power supply system showing theinterconnection of the resonance suppressing apparatus of the presentinvention therewith.

For purposes of illustration in the accompanying drawing, the presentinvention is shown in connection with changes in energization of athree-phase power transformer generally in dicated at (FIG. 3) which iselectrically connected in a main alternating current electrical circuitthrough the use of three primary leads 12, 13, 14. Each primary leadconnects to a corresponding one of three single-phase disconnectswitches or cutouts, 16, l7, 18. As is conventional, the single-phasedisconnect switches incorporate elements electrically connected to theleads 12, 13, 14 and elements electrically connected to the conductorsof the main alternating current electrical circuit, with movablesections provided for connecting and disconnecting these elements andthereby changing the energization of the leads l2, 13, I4 and the powertransformer 10 supplied through the leads. 1

As briefly described above, the leads l2, l3 and 14 and the powertransformer 10 are subject to the appearance therein of ferroresonanceeffects, particularly where the leads l2, l3. 14 pass underground andthe secondary windings of the power transformer 10 are unloaded or atmost very lightly loaded. Such resonance effects appear primarily inview of the capacitance of the leads l2, l3, 14 to electrical ground,set up due to the insulation surrounding the conductors of the leads andindicated schematically in FIG. 3 by the capacitors C2, C3, C4.

In accordance with the present invention, the lead to ground capacitanceof at least two to the underground leads is shunted by the temporaryelectrical connection therewith of resonance suppressing impedancemeans. In order to facilitate ready application of the presentinvention, such means preferably is incorporated in a portable resonancesuppressing apparatus generally indicated at 20. In accordance with thepresent invention, the apparatus 20 comprises a hollow elongate, openended tube 21 of electrically insulating material. Mounted within thetube 21 for cooling air flow therearound is a resonancesuppressingimpedance means 22, preferably in the form of an electrical resistor.

The impedance means 22 is electrically connected in parallel with a leadto ground capacitance through the provision of grounding conductor means24 electrically connected to the impedance means 22 and adapted to beelectrically connected to an electrical ground. Preferably, thegrounding conductor means 24 comprises a length of flexible electricalconductor secured to one end of the tube 21 and a conductive clamp meansmounted at the other end of the flexible conductor for facilitating easein connection thereof with an electrical ground such as a grounding roddriven into the ground adjacent the location of use of the portableresonance suppressing apparatus 20. The'impedance means 22 iselectrically connected with a selected lead through the provision ofelectrically conductive suspension means 28 mounted adjacent the otherend of the tube 21. As illustrated, the suspension means preferablycomprises a hook member for facilitating ease in hanging and removal ofthe apparatus 20, as by suspending the tube 21 from an opening 30provided in or adjacent that portion of a disconnect switchwhich'is'electrically connected with the selected one of the leads l2,13, 14. As will be noted, the suspension means is adapted to hang thetube 21 from the main alternating electrical circuit so as toelectrically connect the impedance means 22 in parallel with thecapacitance C2, C3, C4 of the selected one of the leads 12, 13, 14. Theresulting parallel resistance-capacitance circuit so varies thecharacteristics as to damp any resonance effect otherwise possiblyappearing in the lead upon a change in energization thereof.

In application of the resonance suppressing apparatus 20 describedheretofore, with particular reference to a multiple phase powertransformer, resonance suppressing impedances are temporarilyelectrically connected between each of at least two of the leads and anelectrical ground, thereby connecting the resonance suppressingimpedances in parallel with the capacitance of the at least two leads toground. Energization of the transformer is then changed by firstchanging the energization of the third lead which does not have aresonance suppressing impedance temporarily electrically connectedthereto. Then, the energization of the at least two leads havingimpedances temporarily connected thereto are changed to complete thechange in energization of the power transformer.

The resonance suppressing apparatus are then disconnected from the leadsand may be stored in an equipment truck or automobile pending the nextsubsequent need therefor.

It is to be noted that the method of the present invention is equallyapplicable to the energizing of the leads to efiect energization of thepower transformer and to the de-energizing of the leads to effectde-energization of the power transformer. Further, in instances where asingle-phase distribution network is employed, the present invention isapplied by connecting a resonance suppressing impedance to one of theleads and first changing the energization of the other lead. Thus, thepresent invention will be understood as being applicable to the variouspower distribution approaches presently in use in connection withalternating current electrical power.

In the drawings and specification, there has been set forth a preferredembodiment of the invention, and although specific terms are employed,they are used in a generic and descriptive sense only and not forpurposes of limitation.

What is claimed is:

1. A method of suppressing resonance effects otherwise possiblyoccurring upon a change in energization of an unloaded power transformerhaving leads connected in a main alternating current electrical circuit,the method comprising the steps of temporarily electrically connecting aresonance suppressing impedance between a lead of the unloadedtransformer and an electrical ground, then changing the state ofenergization of the unloaded transformer while damping with theresonance suppressing impedance any resonance effect appearing in thelead, and then removing the resonance suppressing impedance fromconnection with the lead and ground.

2. A method according to claim 1 wherein the temporary connection of theresonance suppressing impedance comprises electrically connecting oneterminal of a resistor to the electrical ground and then electricallyconnecting another terminal of the resistor to the lead so that theresistor is effectively placed in parallel with the capacitance of thelead to the ground.

3. A method of suppressing resonance effects otherwise possiblyoccurring upon a change in energization of an unloaded, multiple phase,power transformer having at least three underground leads connected in amain alternating current electrical circuit, the method comprising thesteps of temporarily electrically connecting resonance suppressingimpedances between each of at least two of the underground leads and anelectrical ground and thereby connecting the resonance suppressingimpedances in parallel with the capacitance of the at least two leads tothe ground, then changing the energization of another underground leadnot having a resonance suppressing impedance temporarily electricallyconnected thereto, then changing the energization of the at least twoleads having resonance suppressing impedance temporarily electricallyconnected thereto to complete the change in energization of the powertransformer, and then disconnecting the resonance suppressing impedancesfrom the at least two leads.

4. A method according to claim 3 wherein the'steps of changingenergization of leads include de-energizing the leads to efiectde-energization of the power transformer.

5. A method according to claim 3 wherein the steps of changingenergization of leads include energizing the leads to effectenergization of the power transformer.

1. A method of suppressing resonance effects otherwise possiblyoccurring upon a change in energization of an unloaded power transformerhaving leads connected in a main alternating current electrical circuit,the method comprising the steps of temporarily electrically connecting aresonance suppressing impedance between a lead of the unloadedtransformer and an electrical ground, then changing the state ofenergization of the unloaded transformer while damping with theresonance suppressing impedance any resonance effect appearing in thelead, and then removing the resonance suppressing impedance fromconnection with the lead and ground.
 2. A method according to claim 1wherein the temporary connection of the resonance suppressing impedancecomprises electrically connecting one terminal of a resistor to theelectrical ground and then electrically connecting another terminal ofthe resistor to the lead so that the resistor is effectively placed inparallel with the capacitance of the lead to the ground.
 3. A method ofsuppressing resonance effects otherwise possibly occurring upon a changein energization of an unloaded, multiple phase, power transformer havingat least three underground leads connected in a main alternating currentelectrical circuit, the method comprising the steps of temporarilyelectrically connecting resonance suppressing impedances between each ofat least two of the underground leads and an electrical ground andthereby connecting the resonance suppressing impedances in parallel withthe capacitance of the at least two leads to the ground, then changingthe energization of another underground lead not having a resonancesuppressing impedance temporarily electrically connected thereto, thenchanging the energization of the at least two leads having resonancesuppressing impedance temporarily electrically connected thereto tocomplete the change in energization of the power transformer, and thendisconnecting the resonance suppressing impedances from the at least twoleads.
 4. A method according to claim 3 wherein the steps of changingenergization of leads include de-energizing the leads to effectde-energization of the power transformer.
 5. A method according to claim3 wherein the steps of changing energization of leads include energizingthe leads to effect energization of the power transformer.